Characterization of mutations in the two‐component histidine kinase gene that confer fludioxonil resistance and osmotic sensitivity in the os‐1 mutants of Neurospora crassa

May 26, 2001Pest management science

Mutations in a key fungal sensor gene linked to fludioxonil resistance and salt sensitivity in Neurospora crassa mutants

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Abstract

Osmotic-sensitive (os-1) mutant alleles in Neurospora crassa show resistance to fungicides, with type I strains exhibiting strong resistance to iprodione and fludioxonil.

Type I os-1 mutants are null mutants, carrying significant mutations that disrupt the osmo-sensing histidine kinase.
Type II strains exhibit sensitivity to osmotic stress due to single amino acid changes in the Os1p protein.
The mutations in type I strains suggest that Os1p is crucial for the antifungal activity of certain fungicides.
Amino acid variations in type II strains are located within tandem repeats of the Os1p protein, indicating a role in osmo-regulation.
Type II strains' increased sensitivity to osmotic stress compared to type I supports the importance of Os1p's structure in regulating osmotic response.

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Osmotic-sensitive (os-1) mutant alleles in Neurospora crassa exhibit resistance to dicarboximides, aromatic hydrocarbons and phenylpyrroles. We have previously reported that the os-1 mutants can be classified into two groups based on their resistance to fungicides and osmotic stress: type I, which are highly resistant to iprodione and fludioxonil but moderately sensitive to osmotic stress, and type II, which are highly sensitive to osmotic stress but moderately resistant to fungicides. To explain the mechanism of resistance to these fungicides, we cloned and sequenced the mutant os-1 genes that encode putative osmo-sensing histidine kinase. Within the os-1 gene product (Os1p), the type I strains, NM233t and Y256M209, carried a stop codon at amino acid position 308 and a frameshift at amino acid position 294, respectively. These mutation sites were located on the upstream of histidine kinase and the response regulator domains of Os1p, strongly suggesting that type I strains are null mutants. The null mutants, NM233t and Y256M209, were highly resistant to iprodione and fludioxonil; thus Os1p is essential for these fungicides to express their antifungal activity. The amino acid changes in Os1p, 625Pro from Leu, 578Val from Ala, and 580Arg from Gly were found in the type II strains, M16, M155-1 and P5990, respectively. Os1p is novel in having six tandem repeats of 90 amino acids in the N terminal. Each amino acid change of the type II strains was located on the fifth unit of six tandem repeats. Type II strains with single amino acid changes were more sensitive to osmotic stress than the null mutants (type I), indicating that the amino acid repeats of Os1p were responsible for an important function in osmo-regulation.

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Characterization of mutations in the two‐component histidine kinase gene that confer fludioxonil resistance and osmotic sensitivity in the os‐1 mutants of Neurospora crassa

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